Existing methods for tracking an individual's vital signs involves either taking time out of their day to use medical devices, or wearing portable ambulatory devices. These methods are intrusive to one's daily life, requiring one to change their lifestyle and habits in order to consistently acquire their medical state.
Historically, there are four measurement techniques that are used for estimation of a pulse wave velocity. First, the clinical gold standard uses tonometry where a transducer is held against the carotid artery (neck) and a thigh pressure cuff is used to measure when the pulse wave reaches the femoral artery. The distance between the two measurement points, coupled with the pulse transit time (PTT) is used to determine an aortic pulse wave velocity (PWV) and estimate aortic compliance. This method requires assistance from medically trained personnel to provide and properly attach the equipment to the patient.
In a second technique, two points on the same artery are used to measure an arterial PTT, with the distance between measurement points determining PWV. This is often done using two photoplethysmography (PPG) sensors with known separation between the two positioned on the radial artery of the arm, or in the finger (using the foot to foot measurement of the two PPG waveforms). However, this technique estimates the PWV in the measured peripheral artery, not in the aorta, and is therefore not useful for determining aortic compliance, but is often used to estimate blood pressure.
In a third technique, the R-wave peak of the ECG is used as the starting point, with a peripheral PPG measurement (often finger, toe, or ear) used as the distal point. This measurement is called the pulse arrival time (PAT) and is often used as a surrogate for PTT (and PWV) in estimating blood pressure. However, as this measurement technique includes the PEP it has no basis in physiology and fundamental pulse wave velocity/blood pressure theory.
In a fourth technique, the BCG is used as the starting point (estimating aortic ejection) and PPG at the periphery (toe) is used as the distal point for estimation of a PWV. This approach measures an averaged PWV of the aorta and femoral artery. It has been used for aortic compliance estimation. However, it is not an accurate measurement of the true aorta PWV due to the contribution of the femoral artery distance from the end of the aorta to the toe.
Chair-based approaches for recording BCG are known to produce waveforms for the same person that are significantly different for various segments of the same recording, severely reducing the diagnostic value of the measurement. Body movements are known to generate stronger signal values than normal cardiac activities during recording causing loss of information and destroying individual BCG cycles.
Currently, the art lacks integration of physiological monitoring into an individual's everyday life without causing them to change their habits or perform any specific task. The art further lacks health condition monitoring techniques that provide a robust measure of aortic PWV without the aid of medical personnel for collection of data. The art lacks the ability for the daily non-invasive medical analysis of the cardiac and vascular functions of an individual.